1. Field of the Invention
The present invention relates to a "J" shaped stiffener wire for use in a cardiac pacing lead such as a lead commonly referred to as a "J" atrial lead. More specifically, the present invention relates to a stiffener wire having a preset "J" shape, which is made of a metal material which returns to the preset shape after being deformed therefrom and which is electrically insulated so that the insulation on the stiffener wire keeps the wire from coming into contact with electrical conductors within the lead thereby to prevent establishment of a secondary electrical conductive path through the wire.
2. Description of the Prior Art
Heretofore various embodiments of curve shaped retainers have been proposed for providing pacing leads having a distal end of a preset shape. Examples of curve shaped retainers are disclosed in the following U.S. Pat. Nos.:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 1,060,665 Bell 4,402,328 Doring 4,454,888 Gold 4,488,561 Doring 4,493,329 Crawford et al. 4,552,157 Littleford 4,567,901 Harris 4,586,923 Gould et al. 4,677,990 Neubauer ______________________________________
The non-analogous Bell U.S. Pat. No. 1,060,665 discloses the use of a stiffening member made of a metal, like tempered piano wire, which may be given a permanent set and which will, if bent only slightly, tend to spring back to the curved form previously given it. The wire is embedded in one wall of a prostatic catheter.
The Doring U.S. Pat. No. 4,402,328 discloses a crista terminalis atrial electrode lead which incorporates a resilient molded Silastic J shaped molding surrounding a pliant catheter and conductor for holding same in a substantial J shape.
The Gold U.S. Pat. No. 4,454,888 discloses a cardiac pacing lead with curve retainer wherein the retainer is formed from a curved flattened spring embedded within the lead body and running along a surface of a coiled conductive wire, to which the spring can be welded in one embodiment of the lead.
The Neubauer U.S. Pat. No. 4,677,990 discloses an endocardial electrode the form of which is controllable to form selected contours by exerting a tension on a freely movable tractional element extending through a channel of the electrode.
The Gould et al. U.S. Pat. No. 4,586,923 discloses a curving tip catheter which includes a wire situated within a passageway and having a distal end thereof coupled to a distal end of a flexible tip portion of the catheter. The wire extends the length of the catheter and the proximal end thereof can be pulled to deform the flexible tip portion of the catheter.
The Harris et al. U.S. Pat. No. 4,567,901 discloses a prebent ventricular/atrial cardiac pacing lead, with the prebent portion being made from a number of curved sections that interact with each other and are preferably integrally molded with each other.
The Littleford U.S. Pat. No. 4,552,157 discloses an open curve, atrial "J" electrode which incorporates direction indicating means and a plastic material having a memory in the body thereof so that, after the electrode is straightened for insertion, the electrode will return to its memorized "J" shape after the straightening element is removed with the direction indicating means defining to the user the position of the tip.
The Crawford U.S. Pat. No. 4,493,329 discloses an implantable electrode having different stiffening and curvature maintaining characteristics along its length. A "J" shaped portion of the electrode includes a spiral multifilar portion wherein the spirally wound filars are interleaved in a juxtapositional relationship to each other to provide a stiff and curved portion to the lead.
The Doring U.S. Pat. No. 4,488,561 discloses a pacing lead with insertable memory coil wherein the coil is monofilar and tends to assume a predetermined bend. The coil is provided with a lumen which receives a straightening stylet therein to aid in insertion of the lead and, once the stylet is removed, the coil returns to its predetermined bent condition.
As will be described in greater detail hereinafter, the "J" stiffener wire of the present invention comprises a noncoiled wire made of a metal material having a "memory" and including means for preventing detachment of the wire from its point of attachment to the lead at the distal end of the lead. The stiffener wire is coated with a tetrafluoroethylene or diparaxylene material to insulate the stiffener wire from the conductors of the catheter surrounding the stiffener wire. Upon flexing of the lead, such as during insertion, the stiffener wire comes into contact with the conductors of the lead, which are preferably electrically insulated, and, but for the insulative covering, could cause a secondary electrical path to form if the stiffener wire is not electrically insulated and could cut through the insulation on the conductors, causing a deviation in the resistance along the primary electrical path along the coiled conductor. The provision of an electrically insulative coating to the stiffener wire eliminates the formation of such secondary electrical pathway.